WO2017136672A1 - Porous silicon structures and laser machining methods for semiconductor wafer processing - Google Patents

Porous silicon structures and laser machining methods for semiconductor wafer processing Download PDF

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Publication number
WO2017136672A1
WO2017136672A1 PCT/US2017/016429 US2017016429W WO2017136672A1 WO 2017136672 A1 WO2017136672 A1 WO 2017136672A1 US 2017016429 W US2017016429 W US 2017016429W WO 2017136672 A1 WO2017136672 A1 WO 2017136672A1
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Prior art keywords
silicon layer
semiconductor wafer
porous silicon
template
silicon
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PCT/US2017/016429
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French (fr)
Inventor
Jonathan S. Frankel
David Masayuki Ishikawa
Fatih Mert OZKESKIN
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Applied Materials, Inc.
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Publication of WO2017136672A1 publication Critical patent/WO2017136672A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1804—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof comprising only elements of Group IV of the Periodic Table
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
    • H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/547—Monocrystalline silicon PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • Embodiments of the present disclosure pertain to the field of semiconductor processing and, in particular, to methods of separating silicon solar cells and dicing semiconductor wafers.
  • wafer processing integrated circuits and solar cells are formed on a wafer (also referred to as a substrate). Each wafer is processed to form a large number of individual solar cells or individual regions containing integrated circuits known as dice. Following the integrated circuit formation process or the solar cell formation process, the wafer is singulated to separate individual dies or individual solar cells from one another. Typical methods that are used for singulation are scribing and sawing. One problem with either scribing or sawing is that chips and gouges can form along the severed edges of the singulated piece. In addition, cracks can form and propagate from the edges of the dice into the substrate and render the integrated circuit inoperative.
  • the inventors have provided improved methods for separating silicon solar cells and dicing semiconductor wafers.
  • a method of separating a silicon solar wafer from atop a silicon template includes: (a) forming a porous silicon layer atop a silicon template; (b) annealing the porous silicon layer to reorganize the porous silicon layer to form a low porosity seed zone and an exfoliation zone; (c) depositing an epitaxial silicon layer atop the reorganized porous silicon layer to form a silicon solar wafer; (d) cutting the silicon solar wafer and the reorganized porous silicon layer along a lateral edge of the silicon template via a water-collimated laser beam without cutting the silicon template; and (e) separating the silicon solar wafer from atop the reorganized porous silicon layer.
  • a method of dicing a semiconductor wafer comprising a plurality of integrated circuits includes: (a) forming porous silicon in device perforation areas between integrated circuits on the semiconductor wafer; (b) applying a thin polyvinyl alcohol (PVA) mask atop the plurality of integrated circuits; (c) cutting the semiconductor wafer to singulate the plurality of integrated circuits.
  • PVA polyvinyl alcohol
  • a method of dicing a semiconductor wafer comprising a plurality of integrated circuits includes: (a) laser scribing the semiconductor wafer to form trenches partially into but not through the semiconductor wafer between the plurality of integrated circuits; (b) cutting the semiconductor wafer via a water-collimated laser beam through the trenches to form corresponding trench extensions and singulate the plurality of integrated circuits.
  • Figure 1 is a flow diagram of a method for separating a silicon solar wafer from atop a silicon template in accordance with some embodiments of the present disclosure.
  • Figures 2A-2E are illustrative cross-sectional views of a substrate during different stages of the method of Figure 1 in accordance with some embodiments of the present disclosure.
  • Figures 3A-3D are illustrative cross-sectional views of a substrate during different stages of the method of Figure 1 in accordance with some embodiments of the present disclosure.
  • Figure 4 is a flow diagram of a method for dicing a semiconductor wafer comprising a plurality of integrated circuits in accordance with some embodiments of the present disclosure.
  • Figures 5A-5C are illustrative cross-sectional views of a substrate during different stages of the method of Figure 4 in accordance with some embodiments of the present disclosure.
  • Figure 6 is a flow diagram of a method for dicing a semiconductor wafer comprising a plurality of integrated circuits in accordance with some embodiments of the present disclosure.
  • Figures 7A-7B are illustrative cross-sectional views of a substrate during different stages of the method of Figure 6 in accordance with some embodiments of the present disclosure.
  • Figure 8 is a flow diagram of a method 800 for processing a substrate in accordance with some embodiments of the present disclosure.
  • Figures 9A-9D are illustrative cross-sectional views of a substrate during different stages of the processing sequence of Figure 8 in accordance with some embodiments of the present disclosure.
  • Embodiments of methods for separating silicon solar cells and dicing semiconductor wafers are provided herein.
  • the inventive methods described herein may advantageously facilitate silicon solar wafer separation using a single water collimated laser cutting process.
  • the water collimated laser advantageously enables solar cell manufacturing with templates and wafers of equal size and without complex and costly focal length adjustment.
  • the inventive methods described herein may also advantageously facilitate die singulation using porous silicon and a water-collimated laser.
  • Use of the porous silicon in die in device perforation areas advantageously reduces chipping and edge cracking along the edges of the integrated circuits during dicing.
  • the water-collimated laser is advantageously material and equipment compatible with back end packaging which makes the water-collimated laser more production worthy than chemical etching for separating a plurality of integrated circuits.
  • Figure 1 is a flow diagram of a method 100 for separating a silicon solar wafer from atop a silicon template in accordance with some embodiments of the present disclosure.
  • Figures 2A-2E are illustrative cross-sectional views of a substrate during different stages of the processing sequence of Figure 1 in accordance with some embodiments of the present disclosure.
  • the method 100 begins at 102, as depicted in Figure 2A, by forming a porous silicon layer 200 atop a silicon template 202.
  • the porous silicon layer 200 is formed by submerging the silicon template 202 in an electrolyte solution and applying an anodic current. Silicon atoms on the surface of the silicon template 202 facing the negative electrode are etched leaving nanometer- scale pores. The thickness and porosity of the porous silicon layer 200 are controlled by the direction and magnitude of the anodic current passing through the thickness of the silicon template 202.
  • the porous silicon layer 200 may have a thickness between about 0.1 micron and about 3 microns and may have porosity between about 25 percent and about 75 percent.
  • the porous silicon layer may be formed using two or more sequential steps with different anodic current and time settings to form a shallow zone with low porosity and a deeper zone with high porosity.
  • the silicon template 202 may first be subjected to a first anodic current for a first period of time to form a shallow zone with low porosity and then subjected to a second anodic current for a second period of time to form a deeper zone with high porosity.
  • the porous silicon layer 200 consists of one or more zones with low porosity and one or more zones with high porosity. As described above, in some embodiments, the porous silicon layer 200 comprises a shallow zone, proximate the upper surface 206 of the porous silicon layer 200, with a low porosity, for example about 25 percent porosity, and a deeper zone with a high porosity, for example about 75 percent porosity.
  • the porous silicon layer 200 is annealed 204. Annealing the porous silicon layer 200 reorganizes the porous silicon layer 200 in zones with low porosity to produce a low porosity seed zone.
  • the low porosity seed zone has a crystalline structure to enhance epitaxial growth of subsequently deposited silicon layer 208 described at 106 below.
  • the anneal process also consolidates the pores in the high porosity zone (i.e. the exfoliation zone) into large voids to assist with wafer separation as described at 1 10 below.
  • the seed zone has a thickness of less than about 1 micron.
  • the exfoliation zone has a thickness of about 1 to about 3 microns.
  • the anneal process occurs in a hydrogen environment at a suitable temperature and for suitable amount of time to reorganize the upper surface 206 of the porous silicon layer 200. For example, in some embodiments, the anneal process occurs at a temperature of about 1 100 to about 1200 degrees Celsius for about 5 to about 30 minutes.
  • a silicon layer 208 is deposited atop the reorganized surface 210 of the porous silicon layer 200 to form a silicon substrate.
  • the silicon layer 208 formed atop the reorganized surface 210 of the porous silicon layer 200 is a solar wafer.
  • the silicon layer 208 is about 40 to about 160 microns thick, for example about 100 microns thick.
  • the silicon layer 208 is deposited atop the reorganized surface 210 of the porous silicon layer 200 via any suitable epitaxial deposition process known in the art.
  • a water-collimated laser beam 212 from a water-collimated laser is used to cut the silicon layer 208 and the porous silicon layer 200 along a lateral edge 214 of the silicon template 202 without cutting the silicon template 202.
  • the water-collimated laser beam 212 is used to cut a bevel 216 along the lateral edge 214 having an angle of about 45 degrees or greater and less than about 90 degrees from a horizontal surface 218 of the silicon layer 208.
  • the water-collimated laser produces a water- collimated laser beam 212 using a liquid source comprising a mixture of water and solvent.
  • the purpose of the solvent is to reduce the surface tension of the water.
  • the mixture comprises about 5 to about 100 percent solvent, for example about 5 vol. % solvent and the balance water.
  • the solvent is isopropanol, toluene, or the like.
  • the mixture reduces the water column diameter to about 5 to about 25 microns, for example about 15 microns.
  • Conventional silicon solar wafer separation utilizes a first IR laser beam having a first wavelength to define a window on the perimeter of a silicon solar cell formed atop a silicon template.
  • the silicon solar cell is then separated from the silicon template.
  • a second laser, having a second wavelength different from the first wavelength, is used to trim the edges of the silicon solar cell to a final controlled dimension.
  • the silicon template can be reclaimed for example via a chemical treatment or ultrasonic treatment.
  • the method 100 advantageously uses a single laser cutting process to separate a silicon solar wafer instead of the conventional dual laser separation processes described above.
  • the use of the water collimated laser also advantageously enables solar cell manufacturing with templates and wafers of equal size instead of using oversized templates as in the conventional process described above.
  • the water-collimated laser minimizes epitaxial silicon redeposition, which improves silicon solar cell yield.
  • the water-collimated laser minimizes the heat affected zone which reduces epitaxial silicon redeposition on the template surface and also reduces cracking at the laser edge, providing significant yield enhancement. Minimizing the heat affected zone also advantageously prevents the porous silicon from fusing to the template which improves the exfoliation yield.
  • the water-collimated laser does not utilize complex and costly focal length adjustment typically used for conventional lasers.
  • the porous silicon layer 200 encompasses an outer surface 300 of the silicon template 202.
  • the porous silicon layer 200 is formed as described above with respect to Figure 2A.
  • the porous silicon layer 200 is annealed, as described at 104 above, to reorganize the surface of the porous silicon layer 200.
  • the silicon layer 208 is formed to encompass an outer surface 302 of the reorganized porous silicon layer 200.
  • the silicon layer 208 and the porous silicon layer 200 are cut via a water-collimated laser beam 212 along the lateral edge 214 of the silicon template 202.
  • the water-collimated laser beam 212 is applied perpendicular to a horizontal surface 218 of the silicon layer 208.
  • the silicon layer 208 i.e. the solar wafer
  • the silicon layer 208 is lifted or peeled from atop the porous silicon layer 200 using for example a vacuum process.
  • Figure 4 is a flow diagram of a method 400 for dicing a semiconductor wafer comprising a plurality of integrated circuits in accordance with some embodiments of the present disclosure.
  • Figures 5A-5D are illustrative cross-sectional views of a substrate during different stages of the processing sequence of Figure 4 in accordance with some embodiments of the present disclosure.
  • the method 400 begins at 402, as depicted in Figure 5A, by forming porous silicon in device perforation areas 506 that separate a plurality of integrated circuits 504.
  • the device perforation areas 506 do not contain integrated circuits 504 and are designated as locations along which the semiconductor wafer 502 will be diced.
  • the device perforation areas 506 are selectively electrochemically etched to form porous silicon. Selective electrochemical etching can be done by using a grid of platinum wire electrodes aligned to the device perforation areas 506.
  • the porous silicon is formed in the device perforation areas 506 by masking the integrated circuits 504 with a patterned mask layer to prevent acid in the electrolyte solution from contacting the integrated circuits 504.
  • the patterned mask layer may be any suitable mask layer such as a hard mask or photoresist layer.
  • the patterned mask layer may be formed by any process suitable to form a patterned mask layer capable of providing an adequate template for defining a pattern. For example, in some embodiments, the patterned mask layer may be formed via a patterned etch process.
  • semiconductor wafer 502 is composed of a material suitable to withstand a fabrication process and upon which semiconductor processing layers may suitably be disposed.
  • semiconductor wafer 502 is composed of a group IV-based material such as, but not limited to, crystalline silicon, germanium or silicon/germanium.
  • providing semiconductor wafer 502 includes providing a monocrystalline silicon substrate.
  • the monocrystalline silicon substrate is doped with impurity atoms.
  • semiconductor wafer 502 is composed of a l l l-V material such as, e.g., a l l l-V material substrate used in the fabrication of light emitting diodes (LEDs).
  • LEDs light emitting diodes
  • semiconductor wafer 502 has disposed, as a portion of the integrated circuits 504, an array of semiconductor devices.
  • semiconductor devices include, but are not limited to, memory devices or complimentary metal-oxide-semiconductor (CMOS) transistors fabricated in a silicon substrate and encased in a dielectric layer.
  • CMOS complimentary metal-oxide-semiconductor
  • a plurality of metal interconnects may be formed above the devices or transistors, and in surrounding dielectric layers, and may be used to electrically couple the devices or transistors to form the integrated circuits 504.
  • Materials making up the device perforation areas 506 may be similar to or the same as those materials used to form the integrated circuits 504.
  • device perforation areas 506 may be composed of layers of dielectric materials, semiconductor materials, and metallization.
  • one or more of the device perforation areas 506 includes test devices similar to the actual devices of the integrated circuits 504.
  • a thin polyvinyl alcohol (PVA) film 500 is applied to the semiconductor wafer 502 to cover the integrated circuits 504.
  • the thickness of the thin PVA film 500 is about 1 to about 2 microns.
  • the purpose of the thin PVA mask is to protect the underlying integrated circuits from damage during the dicing process.
  • the semiconductor wafer 502 is cut at the device perforation areas 506 to singulate the plurality of integrated circuits 504.
  • the semiconductor wafer 502 is cut via any suitable dicing method such as a dicing saw, conventional laser, or a water-collimated laser beam.
  • the thin PVA film 500 is removed following the singulation process. The inventors have observed that the method 400 advantageously improves die yield.
  • the conversion from silicon to porous silicon in the device perforation areas 506 advantageously reduces chipping and edge cracking along the edges of the integrated circuits 504 during dicing.
  • Figure 6 is a flow diagram of a method 600 for dicing a semiconductor wafer comprising a plurality of integrated circuits in accordance with some embodiments of the present disclosure.
  • Figures 7A-7D are illustrative cross-sectional views of a substrate during different stages of the processing sequence of Figure 6 in accordance with some embodiments of the present disclosure.
  • the method 600 begins at 602, as depicted in Figure 7A, laser scribing the semiconductor wafer 700 to form trenches 702 partially into but not through the semiconductor wafer between the plurality of integrated circuits 704.
  • the laser scribing is to a depth at least lower than device layers on the substrate (e.g. , oxide and nitride device layers) and into an underlying bulk silicon.
  • laser scribing is performed using a laser having a pulse width in the femtosecond range.
  • a laser with a wavelength in the visible spectrum plus the ultra-violet (UV) and infra-red (IR) ranges may be used to provide a femtosecond-based laser, i.e., a laser with a pulse width on the order of the femtosecond (e.g., about 10-15 femtoseconds).
  • a femtosecond-based laser i.e., a laser with a pulse width on the order of the femtosecond (e.g., about 10-15 femtoseconds).
  • the semiconductor wafer is cut via a water-collimated laser beam 706 through the trenches 702 to form corresponding trench extensions and singulate the plurality of integrated circuits 704.
  • a thin PVA film can be applied to the semiconductor wafer 700 to cover the integrated circuits 704.
  • the laser scribing at 602 and cutting the semiconductor wafer at 604 are each performed at atmospheric pressure (e.g. , not at vacuum).
  • atmospheric pressure e.g. , not at vacuum
  • the method 600 advantageously improves die yield. Cuts via a water-collimated laser beam 706 have minimal edge cracking, minimal recast, and minimal heat effects on edges between integrated circuits.
  • the water-collimated laser method is material and equipment compatible with back end packaging which makes the water-collimated laser more production worthy than chemical etching for separating a plurality of integrated circuits.
  • the water-collimated laser method has a negligible heat affected zone and therefore does not use a thick PVA mask which reduces the risk of fluorine and carbon contamination.
  • Figure 8 is a flow diagram of a method 800 for processing a substrate in accordance with some embodiments of the present disclosure.
  • Figures 9A-9D are illustrative cross-sectional views of a substrate during different stages of the processing sequence of Figure 8 in accordance with some embodiments of the present disclosure.
  • Embodiments of the method 800 generally relate to methods for processing substrates, and may be useful in processing thin semiconductor substrates.
  • the method may be useful for generating silicon substrates, silicon germanium (SiGe) substrates, or gallium arsenide (GaAs) substrates.
  • Embodiments of the disclosed method may be useful in generating other substrates as well.
  • the inventive methods may advantageously affect production costs by reducing or eliminating waste as compared to some conventional processes used to form thin substrates.
  • a thin substrate is one with a thickness of about 300 pm or less. While not intending to be limiting in scope, the inventors have observed that the inventive methods may be particularly advantageous in the fabrication of mono- crystalline silicon substrates which may be useful in, for example, solar cells.
  • the method begins at 802 by providing a starting double-sided template (template 900), as depicted in Figure 9A, upon which a silicon substrate, for example a solar cell, will be formed.
  • the template 900 is a monocrystalline (100) silicon wafer.
  • the template 900 may be any shape suitable for forming a silicon substrate, such as circular, square, or rectangular.
  • the template 900 may be formed from any process compatible material, including, as non-limiting examples, silicon and gallium-arsenide.
  • the template 900 may have a thickness suitable for forming a silicon substrate.
  • the template 900 comprises a first surface 902, an opposing second surface 904, and an edge 906 connecting the first surface 902 and the second surface 904.
  • the template 900 is a double sided template (e.g. suitable for forming a silicon substrate on the first surface 902 and the second surface 904).
  • the first surface 902 and the second surface 904 are polished, non-textured surfaces.
  • the first surface 902 and the second surface 904 can undergo double sided lapping or buffing processes to produce polished, or substantially polished, and texture-free surfaces.
  • a porous silicon layer 908 is formed on the first surface 902, on the second surface 904, and on the edge 906.
  • Forming the porous silicon layer 908 on the first surface 902 and also on the edge 906 e.g. a "wrap-around" porous silicon layer 908 improves porous silicon quality near the edge of the template 900 and allows the process to be compatible with the epitaxial formation and laser scribing methods described above and depicted in Figures 3A-3D.
  • the porous silicon layer 908 is formed by electrochemical anodic etching of silicon on the first surface 902, on the second surface 904, and on the edge 906.
  • the electrochemical anodic etch is performed by immersing the template in a solution comprising hydrogen fluoride (HF), or hydrogen fluoride (HF) and an acetic acid, or hydrogen fluoride (HF) and isopropyl alcohol (IPA).
  • the solution consists of, or consists essentially of hydrogen fluoride (HF), or hydrogen fluoride (HF) and an acetic acid, or hydrogen fluoride (HF) and isopropyl alcohol (IPA).
  • the electrical current polarity is periodically switched between positive and negative currents so that each side of the template 900 is successively etched in order to form a porous silicon structure on both template sides.
  • the current intensity is also adjusted to form a multilayer porous silicon layer having predetermined different porosities.
  • a high porosity (e.g. 40%-80%) first silicon layer can be formed on the template 900 (e.g. directly on the template 900) to facilitate releasing a subsequently formed semiconductor wafer due to the low-density physical connections and weak mechanical strength of the high porosity first silicon layer and a low porosity (e.g. 15% to 30%) second silicon layer can be formed on the high porosity first silicon layer to act as a crystalline seed layer for subsequent high quality epitaxial silicon growth.
  • An exemplary apparatus for forming a "wrap-around" porous silicon layer 908 is described in commonly owned United States Patent Publication 2016/0298263, entitled “PROCESS GAS PREHEATING SYSTEMS AND METHODS FOR DOUBLE-SIDED MULTI-SUBSTRATE BATCH PROCESSING", by Ishikawa, et al.
  • Each template 900 is held at the second surface 904 proximate the edge 906.
  • holding the templates 900 at the second surface 904 and not at the edge 906 allows for the formation of a "wrap-around" porous silicon layer 908.
  • holding the template at the second surface 904 form an exclusion zone 910 which is an area of the second surface 904 proximate the edge 906 where the porous silicon layer does not form.
  • power supply 1002 provides power with current intensity control, time control, and polarity switching capability to electrodes 1004.
  • the passage of electrical current creates porous silicon layers 908.
  • electrolyte volumes and concentrations, etch chamber sizes, distances between adjacent templates, current levels, and polarities may be used.
  • the template 900 having the porous silicon layer 908 is annealed.
  • the template 900 is annealed at a temperature of about 1000 to about 1300 degrees Celsius.
  • the template is annealed in a hydrogen (H 2 ) gas atmosphere. While annealing, the template 900 is subjected to a gettering process to remove metallic contamination from the template 900.
  • Metallic impurities e.g. platinum from the electrodes 1004; nickel, copper, and iron contamination from walls of the process chamber 1000
  • the gettering process exposes the template 900 to a sufficient temperature for a sufficient amount of time for the metallic impurities in the template 900 to become mobile.
  • the metallic impurities migrate to a location where they are
  • gettering of the template 900 is performed in an atmosphere comprising, or in some embodiments consisting or consisting essentially of, hydrogen chloride (HCI) gas atmosphere at the anneal temperature described above, where the hydrogen chloride (HCL) reacts with metal impurities to form a volatile metal chloride species.
  • gettering of the template 900 is performed in an atmosphere comprising, or in some embodiments consisting or consisting essentially of, trichlorosilane (HC Si) gas and hydrogen (H 2 ) gas at the anneal temperature described above.
  • gettering of the template 900 is performed in an atmosphere comprising, or in some embodiments consisting or consisting essentially of, silicon tetrachloride (SiCI 4 ) gas and hydrogen (H 2 ) gas at the anneal temperature described above.
  • SiCI 4 silicon tetrachloride
  • H 2 hydrogen
  • a silicon layer is epitaxially formed on the template 900.
  • the epitaxial silicon layer 912 is formed on the porous silicon layer 908 at the first surface 902, the second surface 904 (except the exclusion zone 910 of the second surface 904 proximate the edge 906 where the susceptors support the template 900) and the edge 906.
  • the epitaxial silicon layer 912 is via any suitable epitaxial deposition process known in the art
  • the epitaxial silicon layer 912 is formed to a thickness of about 140 to about 160 microns. At the thickness range discussed, the epitaxial silicon layer 912 can be removed from the template as discussed below without the need for reinforcement plates on the epitaxial silicon layer 912.
  • the epitaxial silicon layer 912 is separated (e.g. exfoliated) from the template 900.
  • the epitaxial silicon layer 912 and the porous silicon layer 908 are cut via a water-collimated laser beam along the edge 906 of the template 900.
  • the water-collimated laser beam is applied perpendicular to a horizontal surface of the epitaxial silicon layer 912.
  • the epitaxial silicon layer 912 is lifted or peeled from atop the porous silicon layer 908 using for example a vacuum process.
  • an anisotropic etch may be performed to clear residual reorganized porous silicon material proximate the edge 906 of the template 900 prior to exfoliation at 810 to prevent breakage of the epitaxial silicon layer 912 during exfoliation.
  • the laser scribed epitaxial silicon layer 912 is placed in a reclamation chemistry and prior to initiating exfoliation which improves exfoliation yield without the need for a separate etch bath.
  • Thin epitaxial silicon layer 912 can be allowed to float in the reclamation chemistry after separation, and then mounted to an adhesive-backed film.
  • the exfoliated epitaxial silicon layer 912 is textured via isotexture etching on one or both surfaces 914, 916 of the epitaxial silicon layer 912.
  • the advantage of texturing the epitaxial silicon layer 912 after exfoliation is provide a smooth emitter-face and improved process control of the texture process.

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Abstract

In some embodiments, a method of separating a silicon solar wafer from atop a silicon template includes: (a) forming a porous silicon layer atop a silicon template; (b) annealing the porous silicon layer to reorganize the porous silicon layer to form a low porosity seed zone and an exfoliation zone; (c) depositing an epitaxial silicon layer atop the reorganized porous silicon layer to form a silicon solar wafer; (d) cutting the silicon solar wafer and the reorganized porous silicon layer along a lateral edge of the silicon template via a water-collimated laser beam without cutting the silicon template; and (e) separating the silicon solar wafer from atop the reorganized porous silicon layer.

Description

POROUS SILICON STRUCTURES AND LASER MACHINING METHODS FOR SEMICONDUCTOR WAFER PROCESSING
FIELD
[0001] Embodiments of the present disclosure pertain to the field of semiconductor processing and, in particular, to methods of separating silicon solar cells and dicing semiconductor wafers.
BACKGROUND
[0002] In semiconductor wafer processing, integrated circuits and solar cells are formed on a wafer (also referred to as a substrate). Each wafer is processed to form a large number of individual solar cells or individual regions containing integrated circuits known as dice. Following the integrated circuit formation process or the solar cell formation process, the wafer is singulated to separate individual dies or individual solar cells from one another. Typical methods that are used for singulation are scribing and sawing. One problem with either scribing or sawing is that chips and gouges can form along the severed edges of the singulated piece. In addition, cracks can form and propagate from the edges of the dice into the substrate and render the integrated circuit inoperative.
[0003] Thus, the inventors have provided improved methods for separating silicon solar cells and dicing semiconductor wafers.
SUMMARY
[0004] In some embodiments, a method of separating a silicon solar wafer from atop a silicon template includes: (a) forming a porous silicon layer atop a silicon template; (b) annealing the porous silicon layer to reorganize the porous silicon layer to form a low porosity seed zone and an exfoliation zone; (c) depositing an epitaxial silicon layer atop the reorganized porous silicon layer to form a silicon solar wafer; (d) cutting the silicon solar wafer and the reorganized porous silicon layer along a lateral edge of the silicon template via a water-collimated laser beam without cutting the silicon template; and (e) separating the silicon solar wafer from atop the reorganized porous silicon layer. [0005] In some embodiments, a method of dicing a semiconductor wafer comprising a plurality of integrated circuits includes: (a) forming porous silicon in device perforation areas between integrated circuits on the semiconductor wafer; (b) applying a thin polyvinyl alcohol (PVA) mask atop the plurality of integrated circuits; (c) cutting the semiconductor wafer to singulate the plurality of integrated circuits.
[0006] In some embodiments, a method of dicing a semiconductor wafer comprising a plurality of integrated circuits, includes: (a) laser scribing the semiconductor wafer to form trenches partially into but not through the semiconductor wafer between the plurality of integrated circuits; (b) cutting the semiconductor wafer via a water-collimated laser beam through the trenches to form corresponding trench extensions and singulate the plurality of integrated circuits.
[0007] Other embodiments and variations of the present disclosure are discussed below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Embodiments of the present disclosure, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the disclosure depicted in the appended drawings. The appended drawings illustrate only typical embodiments of the disclosure and are therefore not to be considered limiting of the scope, for the disclosure may admit to other equally effective embodiments.
[0009] Figure 1 is a flow diagram of a method for separating a silicon solar wafer from atop a silicon template in accordance with some embodiments of the present disclosure.
[0010] Figures 2A-2E are illustrative cross-sectional views of a substrate during different stages of the method of Figure 1 in accordance with some embodiments of the present disclosure.
[0011] Figures 3A-3D are illustrative cross-sectional views of a substrate during different stages of the method of Figure 1 in accordance with some embodiments of the present disclosure. [0012] Figure 4 is a flow diagram of a method for dicing a semiconductor wafer comprising a plurality of integrated circuits in accordance with some embodiments of the present disclosure.
[0013] Figures 5A-5C are illustrative cross-sectional views of a substrate during different stages of the method of Figure 4 in accordance with some embodiments of the present disclosure.
[0014] Figure 6 is a flow diagram of a method for dicing a semiconductor wafer comprising a plurality of integrated circuits in accordance with some embodiments of the present disclosure.
[0015] Figures 7A-7B are illustrative cross-sectional views of a substrate during different stages of the method of Figure 6 in accordance with some embodiments of the present disclosure.
[0016] Figure 8 is a flow diagram of a method 800 for processing a substrate in accordance with some embodiments of the present disclosure.
[0017] Figures 9A-9D are illustrative cross-sectional views of a substrate during different stages of the processing sequence of Figure 8 in accordance with some embodiments of the present disclosure.
[0018] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. Elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
DETAILED DESCRIPTION
[0019] Embodiments of methods for separating silicon solar cells and dicing semiconductor wafers are provided herein. In at least some embodiments, the inventive methods described herein may advantageously facilitate silicon solar wafer separation using a single water collimated laser cutting process. The water collimated laser advantageously enables solar cell manufacturing with templates and wafers of equal size and without complex and costly focal length adjustment. In at least some embodiments, the inventive methods described herein may also advantageously facilitate die singulation using porous silicon and a water-collimated laser. Use of the porous silicon in die in device perforation areas advantageously reduces chipping and edge cracking along the edges of the integrated circuits during dicing. Furthermore, the water-collimated laser is advantageously material and equipment compatible with back end packaging which makes the water-collimated laser more production worthy than chemical etching for separating a plurality of integrated circuits.
[0020] Figure 1 is a flow diagram of a method 100 for separating a silicon solar wafer from atop a silicon template in accordance with some embodiments of the present disclosure. Figures 2A-2E are illustrative cross-sectional views of a substrate during different stages of the processing sequence of Figure 1 in accordance with some embodiments of the present disclosure.
[0021] The method 100 begins at 102, as depicted in Figure 2A, by forming a porous silicon layer 200 atop a silicon template 202. In some embodiments, the porous silicon layer 200 is formed by submerging the silicon template 202 in an electrolyte solution and applying an anodic current. Silicon atoms on the surface of the silicon template 202 facing the negative electrode are etched leaving nanometer- scale pores. The thickness and porosity of the porous silicon layer 200 are controlled by the direction and magnitude of the anodic current passing through the thickness of the silicon template 202. The porous silicon layer 200 may have a thickness between about 0.1 micron and about 3 microns and may have porosity between about 25 percent and about 75 percent. In some, embodiments, the porous silicon layer may be formed using two or more sequential steps with different anodic current and time settings to form a shallow zone with low porosity and a deeper zone with high porosity. For example, the silicon template 202 may first be subjected to a first anodic current for a first period of time to form a shallow zone with low porosity and then subjected to a second anodic current for a second period of time to form a deeper zone with high porosity.
[0022] The porous silicon layer 200 consists of one or more zones with low porosity and one or more zones with high porosity. As described above, in some embodiments, the porous silicon layer 200 comprises a shallow zone, proximate the upper surface 206 of the porous silicon layer 200, with a low porosity, for example about 25 percent porosity, and a deeper zone with a high porosity, for example about 75 percent porosity. At 104, and as depicted in Figure 2B, the porous silicon layer 200 is annealed 204. Annealing the porous silicon layer 200 reorganizes the porous silicon layer 200 in zones with low porosity to produce a low porosity seed zone. The low porosity seed zone has a crystalline structure to enhance epitaxial growth of subsequently deposited silicon layer 208 described at 106 below. The anneal process also consolidates the pores in the high porosity zone (i.e. the exfoliation zone) into large voids to assist with wafer separation as described at 1 10 below. In some embodiments, the seed zone has a thickness of less than about 1 micron. In some embodiments, the exfoliation zone has a thickness of about 1 to about 3 microns. The anneal process occurs in a hydrogen environment at a suitable temperature and for suitable amount of time to reorganize the upper surface 206 of the porous silicon layer 200. For example, in some embodiments, the anneal process occurs at a temperature of about 1 100 to about 1200 degrees Celsius for about 5 to about 30 minutes.
[0023] Next, at 106, as depicted in Figure 2C, a silicon layer 208 is deposited atop the reorganized surface 210 of the porous silicon layer 200 to form a silicon substrate. In some embodiments, the silicon layer 208 formed atop the reorganized surface 210 of the porous silicon layer 200 (e.g., the silicon substrate) is a solar wafer. In some embodiments, the silicon layer 208 is about 40 to about 160 microns thick, for example about 100 microns thick. In some embodiments, the silicon layer 208 is deposited atop the reorganized surface 210 of the porous silicon layer 200 via any suitable epitaxial deposition process known in the art.
[0024] Next, at 108, as depicted in Figure 2D, a water-collimated laser beam 212 from a water-collimated laser is used to cut the silicon layer 208 and the porous silicon layer 200 along a lateral edge 214 of the silicon template 202 without cutting the silicon template 202. In some embodiments, the water-collimated laser beam 212 is used to cut a bevel 216 along the lateral edge 214 having an angle of about 45 degrees or greater and less than about 90 degrees from a horizontal surface 218 of the silicon layer 208.
[0025] In some embodiments, the water-collimated laser produces a water- collimated laser beam 212 using a liquid source comprising a mixture of water and solvent. The purpose of the solvent is to reduce the surface tension of the water. In some embodiments, the mixture comprises about 5 to about 100 percent solvent, for example about 5 vol. % solvent and the balance water. In some embodiments, the solvent is isopropanol, toluene, or the like. In some embodiments, the mixture reduces the water column diameter to about 5 to about 25 microns, for example about 15 microns.
[0026] Conventional silicon solar wafer separation utilizes a first IR laser beam having a first wavelength to define a window on the perimeter of a silicon solar cell formed atop a silicon template. The silicon solar cell is then separated from the silicon template. A second laser, having a second wavelength different from the first wavelength, is used to trim the edges of the silicon solar cell to a final controlled dimension. The silicon template can be reclaimed for example via a chemical treatment or ultrasonic treatment.
[0027] The inventors have observed that the method 100 advantageously uses a single laser cutting process to separate a silicon solar wafer instead of the conventional dual laser separation processes described above. The use of the water collimated laser also advantageously enables solar cell manufacturing with templates and wafers of equal size instead of using oversized templates as in the conventional process described above.
[0028] In addition, directing the water-collimated laser along the lateral edge of the silicon template (i.e., off the field defined by the template), minimizes epitaxial silicon redeposition, which improves silicon solar cell yield. Another advantage of the method 100 described above is that the water-collimated laser minimizes the heat affected zone which reduces epitaxial silicon redeposition on the template surface and also reduces cracking at the laser edge, providing significant yield enhancement. Minimizing the heat affected zone also advantageously prevents the porous silicon from fusing to the template which improves the exfoliation yield. Another advantage of the method 100 described above is that the water-collimated laser does not utilize complex and costly focal length adjustment typically used for conventional lasers. [0029] Next, at 1 10, as depicted in Figure 2E, the silicon layer 208 (e.g. , the solar wafer) is lifted or peeled from atop the porous silicon layer 200 using for example a vacuum process.
[0030] In some embodiments, at 102, as depicted in Figure 3A, the porous silicon layer 200 encompasses an outer surface 300 of the silicon template 202. The porous silicon layer 200 is formed as described above with respect to Figure 2A. The porous silicon layer 200 is annealed, as described at 104 above, to reorganize the surface of the porous silicon layer 200. In some embodiments, at 106 and as depicted in Figure 3B, the silicon layer 208 is formed to encompass an outer surface 302 of the reorganized porous silicon layer 200. In some embodiments, at 108 and as depicted in Figure 3C, the silicon layer 208 and the porous silicon layer 200 are cut via a water-collimated laser beam 212 along the lateral edge 214 of the silicon template 202. The water-collimated laser beam 212 is applied perpendicular to a horizontal surface 218 of the silicon layer 208. At 1 10 and as depicted in Figure 3D, the silicon layer 208 (i.e. the solar wafer) is lifted or peeled from atop the porous silicon layer 200 using for example a vacuum process.
[0031] Figure 4 is a flow diagram of a method 400 for dicing a semiconductor wafer comprising a plurality of integrated circuits in accordance with some embodiments of the present disclosure. Figures 5A-5D are illustrative cross-sectional views of a substrate during different stages of the processing sequence of Figure 4 in accordance with some embodiments of the present disclosure.
[0032] The method 400 begins at 402, as depicted in Figure 5A, by forming porous silicon in device perforation areas 506 that separate a plurality of integrated circuits 504.
[0033] The device perforation areas 506 do not contain integrated circuits 504 and are designated as locations along which the semiconductor wafer 502 will be diced.
In some embodiments, the device perforation areas 506 are selectively electrochemically etched to form porous silicon. Selective electrochemical etching can be done by using a grid of platinum wire electrodes aligned to the device perforation areas 506. In some embodiments, the porous silicon is formed in the device perforation areas 506 by masking the integrated circuits 504 with a patterned mask layer to prevent acid in the electrolyte solution from contacting the integrated circuits 504. The patterned mask layer may be any suitable mask layer such as a hard mask or photoresist layer. The patterned mask layer may be formed by any process suitable to form a patterned mask layer capable of providing an adequate template for defining a pattern. For example, in some embodiments, the patterned mask layer may be formed via a patterned etch process.
[0034] In an embodiment, semiconductor wafer 502 is composed of a material suitable to withstand a fabrication process and upon which semiconductor processing layers may suitably be disposed. For example, in one embodiment, semiconductor wafer 502 is composed of a group IV-based material such as, but not limited to, crystalline silicon, germanium or silicon/germanium. In a specific embodiment, providing semiconductor wafer 502 includes providing a monocrystalline silicon substrate. In a particular embodiment, the monocrystalline silicon substrate is doped with impurity atoms. In another embodiment, semiconductor wafer 502 is composed of a l l l-V material such as, e.g., a l l l-V material substrate used in the fabrication of light emitting diodes (LEDs).
[0035] In an embodiment, semiconductor wafer 502 has disposed, as a portion of the integrated circuits 504, an array of semiconductor devices. Examples of such semiconductor devices include, but are not limited to, memory devices or complimentary metal-oxide-semiconductor (CMOS) transistors fabricated in a silicon substrate and encased in a dielectric layer. A plurality of metal interconnects may be formed above the devices or transistors, and in surrounding dielectric layers, and may be used to electrically couple the devices or transistors to form the integrated circuits 504. Materials making up the device perforation areas 506 may be similar to or the same as those materials used to form the integrated circuits 504. For example, device perforation areas 506 may be composed of layers of dielectric materials, semiconductor materials, and metallization. In one embodiment, one or more of the device perforation areas 506 includes test devices similar to the actual devices of the integrated circuits 504.
[0036] Next, at 404, and depicted in 5A, a thin polyvinyl alcohol (PVA) film 500 is applied to the semiconductor wafer 502 to cover the integrated circuits 504. In some embodiments, the thickness of the thin PVA film 500 is about 1 to about 2 microns. The purpose of the thin PVA mask is to protect the underlying integrated circuits from damage during the dicing process.
[0037] Next, at 406, and as depicted at Figure 5B, the semiconductor wafer 502 is cut at the device perforation areas 506 to singulate the plurality of integrated circuits 504. In some embodiments, the semiconductor wafer 502 is cut via any suitable dicing method such as a dicing saw, conventional laser, or a water-collimated laser beam. As depicted in 5C, the thin PVA film 500 is removed following the singulation process. The inventors have observed that the method 400 advantageously improves die yield. The conversion from silicon to porous silicon in the device perforation areas 506 advantageously reduces chipping and edge cracking along the edges of the integrated circuits 504 during dicing.
[0038] Figure 6 is a flow diagram of a method 600 for dicing a semiconductor wafer comprising a plurality of integrated circuits in accordance with some embodiments of the present disclosure. Figures 7A-7D are illustrative cross-sectional views of a substrate during different stages of the processing sequence of Figure 6 in accordance with some embodiments of the present disclosure.
[0039] The method 600 begins at 602, as depicted in Figure 7A, laser scribing the semiconductor wafer 700 to form trenches 702 partially into but not through the semiconductor wafer between the plurality of integrated circuits 704. In some embodiments, the laser scribing is to a depth at least lower than device layers on the substrate (e.g. , oxide and nitride device layers) and into an underlying bulk silicon. In some embodiments, laser scribing is performed using a laser having a pulse width in the femtosecond range. Specifically, a laser with a wavelength in the visible spectrum plus the ultra-violet (UV) and infra-red (IR) ranges (totaling a broadband optical spectrum) may be used to provide a femtosecond-based laser, i.e., a laser with a pulse width on the order of the femtosecond (e.g., about 10-15 femtoseconds). Next at 604, and as depicted in Figure 7B, the semiconductor wafer is cut via a water-collimated laser beam 706 through the trenches 702 to form corresponding trench extensions and singulate the plurality of integrated circuits 704. In some embodiments, a thin PVA film can be applied to the semiconductor wafer 700 to cover the integrated circuits 704. In some embodiments, the laser scribing at 602 and cutting the semiconductor wafer at 604 are each performed at atmospheric pressure (e.g. , not at vacuum). The inventors have observed that the method 600 advantageously improves die yield. Cuts via a water-collimated laser beam 706 have minimal edge cracking, minimal recast, and minimal heat effects on edges between integrated circuits. Furthermore, the water-collimated laser method is material and equipment compatible with back end packaging which makes the water-collimated laser more production worthy than chemical etching for separating a plurality of integrated circuits. For example, the water-collimated laser method has a negligible heat affected zone and therefore does not use a thick PVA mask which reduces the risk of fluorine and carbon contamination.
[0040] Figure 8 is a flow diagram of a method 800 for processing a substrate in accordance with some embodiments of the present disclosure. Figures 9A-9D are illustrative cross-sectional views of a substrate during different stages of the processing sequence of Figure 8 in accordance with some embodiments of the present disclosure.
[0041] Embodiments of the method 800 generally relate to methods for processing substrates, and may be useful in processing thin semiconductor substrates. For example and without limitation, the method may be useful for generating silicon substrates, silicon germanium (SiGe) substrates, or gallium arsenide (GaAs) substrates. Embodiments of the disclosed method may be useful in generating other substrates as well. In at least some embodiments, the inventive methods may advantageously affect production costs by reducing or eliminating waste as compared to some conventional processes used to form thin substrates. In some embodiments, a thin substrate is one with a thickness of about 300 pm or less. While not intending to be limiting in scope, the inventors have observed that the inventive methods may be particularly advantageous in the fabrication of mono- crystalline silicon substrates which may be useful in, for example, solar cells.
[0042] The method begins at 802 by providing a starting double-sided template (template 900), as depicted in Figure 9A, upon which a silicon substrate, for example a solar cell, will be formed. In some embodiments, the template 900 is a monocrystalline (100) silicon wafer. The template 900 may be any shape suitable for forming a silicon substrate, such as circular, square, or rectangular. The template 900 may be formed from any process compatible material, including, as non-limiting examples, silicon and gallium-arsenide. The template 900 may have a thickness suitable for forming a silicon substrate. The template 900 comprises a first surface 902, an opposing second surface 904, and an edge 906 connecting the first surface 902 and the second surface 904. The template 900 is a double sided template (e.g. suitable for forming a silicon substrate on the first surface 902 and the second surface 904). The first surface 902 and the second surface 904 are polished, non-textured surfaces. The first surface 902 and the second surface 904 can undergo double sided lapping or buffing processes to produce polished, or substantially polished, and texture-free surfaces.
[0043] Next at 804, and as depicted in Figure 9B, a porous silicon layer 908 is formed on the first surface 902, on the second surface 904, and on the edge 906. Forming the porous silicon layer 908 on the first surface 902 and also on the edge 906 (e.g. a "wrap-around" porous silicon layer 908) improves porous silicon quality near the edge of the template 900 and allows the process to be compatible with the epitaxial formation and laser scribing methods described above and depicted in Figures 3A-3D.
[0044] The porous silicon layer 908 is formed by electrochemical anodic etching of silicon on the first surface 902, on the second surface 904, and on the edge 906. In some embodiments, the electrochemical anodic etch is performed by immersing the template in a solution comprising hydrogen fluoride (HF), or hydrogen fluoride (HF) and an acetic acid, or hydrogen fluoride (HF) and isopropyl alcohol (IPA). In some embodiments, the solution consists of, or consists essentially of hydrogen fluoride (HF), or hydrogen fluoride (HF) and an acetic acid, or hydrogen fluoride (HF) and isopropyl alcohol (IPA). During the porous silicon formation, the electrical current polarity is periodically switched between positive and negative currents so that each side of the template 900 is successively etched in order to form a porous silicon structure on both template sides. In some embodiments, the current intensity is also adjusted to form a multilayer porous silicon layer having predetermined different porosities. For example, a high porosity (e.g. 40%-80%) first silicon layer can be formed on the template 900 (e.g. directly on the template 900) to facilitate releasing a subsequently formed semiconductor wafer due to the low-density physical connections and weak mechanical strength of the high porosity first silicon layer and a low porosity (e.g. 15% to 30%) second silicon layer can be formed on the high porosity first silicon layer to act as a crystalline seed layer for subsequent high quality epitaxial silicon growth.
[0045] An exemplary apparatus for forming a "wrap-around" porous silicon layer 908 is described in commonly owned United States Patent Publication 2016/0298263, entitled "PROCESS GAS PREHEATING SYSTEMS AND METHODS FOR DOUBLE-SIDED MULTI-SUBSTRATE BATCH PROCESSING", by Ishikawa, et al. Each template 900 is held at the second surface 904 proximate the edge 906. As described above, holding the templates 900 at the second surface 904 and not at the edge 906 allows for the formation of a "wrap-around" porous silicon layer 908. However, holding the template at the second surface 904 form an exclusion zone 910 which is an area of the second surface 904 proximate the edge 906 where the porous silicon layer does not form.
[0046] Returning to Figure 10, power supply 1002 provides power with current intensity control, time control, and polarity switching capability to electrodes 1004. The passage of electrical current creates porous silicon layers 908. One of ordinary skill will understand that different electrolyte volumes and concentrations, etch chamber sizes, distances between adjacent templates, current levels, and polarities may be used.
[0047] Next at 806, the template 900 having the porous silicon layer 908 is annealed. The template 900 is annealed at a temperature of about 1000 to about 1300 degrees Celsius. The template is annealed in a hydrogen (H2) gas atmosphere. While annealing, the template 900 is subjected to a gettering process to remove metallic contamination from the template 900. Metallic impurities (e.g. platinum from the electrodes 1004; nickel, copper, and iron contamination from walls of the process chamber 1000) can contaminate the template 900 during the anodic etch process discussed at 804 above.
[0048] The gettering process exposes the template 900 to a sufficient temperature for a sufficient amount of time for the metallic impurities in the template 900 to become mobile. The metallic impurities migrate to a location where they are
"gettered" (i.e. rendered electrically inactive or removed from the active region). In some embodiments, gettering of the template 900 is performed in an atmosphere comprising, or in some embodiments consisting or consisting essentially of, hydrogen chloride (HCI) gas atmosphere at the anneal temperature described above, where the hydrogen chloride (HCL) reacts with metal impurities to form a volatile metal chloride species. In some embodiments, gettering of the template 900 is performed in an atmosphere comprising, or in some embodiments consisting or consisting essentially of, trichlorosilane (HC Si) gas and hydrogen (H2) gas at the anneal temperature described above. In some embodiments, gettering of the template 900 is performed in an atmosphere comprising, or in some embodiments consisting or consisting essentially of, silicon tetrachloride (SiCI4) gas and hydrogen (H2) gas at the anneal temperature described above.
[0049] Next at 808, and as depicted in Figure 9C, a silicon layer is epitaxially formed on the template 900. The epitaxial silicon layer 912 is formed on the porous silicon layer 908 at the first surface 902, the second surface 904 (except the exclusion zone 910 of the second surface 904 proximate the edge 906 where the susceptors support the template 900) and the edge 906. In some embodiments, the epitaxial silicon layer 912 is via any suitable epitaxial deposition process known in the art In some embodiments, the epitaxial silicon layer 912 is formed to a thickness of about 140 to about 160 microns. At the thickness range discussed, the epitaxial silicon layer 912 can be removed from the template as discussed below without the need for reinforcement plates on the epitaxial silicon layer 912.
[0050] Next at 810, and as depicted in Figure 9D, the epitaxial silicon layer 912 is separated (e.g. exfoliated) from the template 900. As described above with respect to Figure 3C-3D, the epitaxial silicon layer 912 and the porous silicon layer 908 are cut via a water-collimated laser beam along the edge 906 of the template 900. The water-collimated laser beam is applied perpendicular to a horizontal surface of the epitaxial silicon layer 912. The epitaxial silicon layer 912 is lifted or peeled from atop the porous silicon layer 908 using for example a vacuum process.
[0051] In some embodiments, an anisotropic etch may be performed to clear residual reorganized porous silicon material proximate the edge 906 of the template 900 prior to exfoliation at 810 to prevent breakage of the epitaxial silicon layer 912 during exfoliation. The laser scribed epitaxial silicon layer 912 is placed in a reclamation chemistry and prior to initiating exfoliation which improves exfoliation yield without the need for a separate etch bath. Thin epitaxial silicon layer 912 can be allowed to float in the reclamation chemistry after separation, and then mounted to an adhesive-backed film.
[0052] Next, at 812 the exfoliated epitaxial silicon layer 912 is textured via isotexture etching on one or both surfaces 914, 916 of the epitaxial silicon layer 912. The advantage of texturing the epitaxial silicon layer 912 after exfoliation is provide a smooth emitter-face and improved process control of the texture process.
[0053] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof.

Claims

Claims:
1 . A method of separating a silicon substrate from atop a silicon template, comprising:
(a) forming a porous silicon layer atop a silicon template;
(b) annealing the porous silicon layer to reorganize the porous silicon layer to form a low porosity seed zone and an exfoliation zone;
(c) depositing an epitaxial silicon layer atop the reorganized porous silicon layer to form a silicon substrate;
(d) cutting the silicon substrate and the reorganized porous silicon layer along a lateral edge of the silicon template via a water-collimated laser beam without cutting the silicon template; and
(e) separating the silicon substrate from atop the reorganized porous silicon layer.
2. The method of claim 1 , wherein forming the porous silicon layer further comprises forming a porous silicon layer atop an upper surface of the silicon template.
3. The method of claim 2, wherein cutting the epitaxial silicon layer and the porous silicon layer further comprises forming a bevel along the lateral edge having an angle of about 45 degrees or greater and less than about 90 degrees from a horizontal surface of the epitaxial silicon layer.
4. The method of claim 1 , wherein forming the porous silicon layer further comprises forming a porous silicon layer encompassing an outer surface of the silicon template.
5. The method of claim 4, wherein forming the epitaxial silicon layer further comprises forming the epitaxial silicon layer encompassing an outer surface of the porous silicon layer.
6. The method of claim 5, wherein cutting the epitaxial silicon layer and the porous silicon layer further comprises applying a water-collimated laser beam along the lateral edge of the silicon template and perpendicular to a horizontal surface of the epitaxial silicon layer.
7. The method of claim 1 , wherein the water-collimated laser beam uses a liquid source comprising a mixture of water and solvent.
8. The method of claim 7, wherein the mixture comprises about 5 to about 100 percent solvent and a balance water.
9. The method of claim 1 , where in the silicon substrate is a silicon solar wafer.
10. A method of dicing a semiconductor wafer comprising a plurality of integrated circuits, the method comprising:
(a) forming porous silicon in device perforation areas between a plurality of integrated circuits on the semiconductor wafer;
(b) applying a thin polyvinyl alcohol (PVA) mask atop the plurality of integrated circuits; and
(c) cutting the semiconductor wafer to singulate the plurality of integrated circuits.
1 1 . The method of claim 10, wherein cutting the semiconductor wafer further comprises cutting the semiconductor wafer via a dicing saw.
12. The method of claim 10, wherein cutting the semiconductor wafer further comprises cutting the semiconductor wafer via a water-collimated laser beam.
13. A method of dicing a semiconductor wafer comprising a plurality of integrated circuits, the method comprising:
(a) laser scribing the semiconductor wafer to form trenches partially into but not through the semiconductor wafer between the plurality of integrated circuits; and (b) cutting the semiconductor wafer via a water-collimated laser beam through the trenches to form corresponding trench extensions and singulate the plurality of integrated circuits.
14. The method of claim 13, wherein the laser scribing and the cutting are performed at atmospheric pressure.
15. The method of claim 13, wherein the laser scribing is to a depth passing through device layers formed on the semiconductor wafer and partially into a bulk silicon of the semiconductor wafer.
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